Survival of habitable planets in unstable planetary systems

TL;DR

This paper models how dynamical instabilities in planetary systems affect the survival of habitable planets, revealing that giant planet architecture and eccentricity critically influence habitability resilience.

Contribution

It introduces a model linking giant planet orbital properties to habitable planet survival, highlighting the impact of planetary mass distribution and eccentricity on habitability outcomes.

Findings

Higher giant planet eccentricity reduces habitable planet survival.

Unequal-mass giant systems are less destructive to habitable planets.

Eccentricity above 0.4 correlates with almost no habitable interior planets.

Abstract

Many observed giant planets lie on eccentric orbits. Such orbits could be the result of strong scatterings with other giant planets. The same dynamical instability that produces these scatterings may also cause habitable planets in interior orbits to become ejected, destroyed, or be transported out of the habitable zone. We say that a habitable planet has resilient habitability if it is able to avoid ejections and collisions and its orbit remains inside the habitable zone. Here we model the orbital evolution of rocky planets in planetary systems where giant planets become dynamically unstable. We measure the resilience of habitable planets as a function of the observed, present-day masses and orbits of the giant planets. We find that the survival rate of habitable planets depends strongly on the giant planet architecture. Equal-mass planetary systems are far more destructive than systems with giant planets of unequal masses. We also establish a link with observation; we find that giant planets with present-day eccentricities higher than 0.4 almost never have a habitable interior planet. For a giant planet with an present-day eccentricity of 0.2 and semimajor axis of 5 AU orbiting a Sun-like star, 50% of the orbits in the habitable zone are resilient to the instability. As semimajor axis increases and eccentricity decreases, a higher fraction of habitable planets survive and remain habitable. However, if the habitable planet has rocky siblings, there is a significant risk of rocky planet collisions that would sterilize the planet.